The present invention relates to architectural lighting, and more particularly to luminaires which are suspended or mounted to a building's architecture to provide an indirect lighting environment. The invention still more particularly relates to the practice of introducing source brightness in an indirectly lit space, and the problems associated with providing exposed specular reflector surfaces for this purpose as disclosed in U.S. Pat. No. 4,866,584, issued to Dale Plewman.
The Plewman patent discloses an indirect luminaire having a dual reflector system featuring an exposed upper parabolic reflector positioned close to the light source to spread source light in a wide distribution pattern and to prevent "hot spots" on the ceiling. The exposed reflector of the Plewman luminaire also directs a small amount of source light in a downward direction below the horizontal in order to introduce a source of observable surface brightness to the architectural space below the luminaire. The introduction of an element of visible and controlled source brightness from an exposed optical element of an indirect luminaire is known to counteract the dullness normally associated with indirect lighting and is known to enhance the visual environment.
The problem with the dual reflector system disclosed in the Plewman patent is that the reflecting surfaces of the exposed upper reflector element are specular and very sensitive to positioning errors. Any errors in the positioning of the reflector can lead to "flashing" below the horizontal, that is, the introduction of visible areas of very high luminance within observable viewing angles below the luminaire. Flashes of high luminance on exposed surfaces produce glare on work surfaces and VDT screens, and further produce excessive brightness that will be uncomfortable to look at when viewed directly. Thus, to prevent flashing, the contoured reflector surfaces of the Plewman upper reflector must be precisely positioned and carefully designed and manufactured. Even then, flashing can occur if the upper reflector or the luminaire is moved slightly from its intended position, such as might occur if a maintenance person causes the luminaire to tilt or knocks the upper reflector element slightly out of position. Moreover, if the two symmetric, parabolic surfaces of the Plewman upper reflector are not matched very carefully, there will be a visually noticeable difference in their behavior which will produce an undesirable asymmetry to the luminaire's performance.
The present invention overcomes the disadvantages of using exposed specular reflectors to introduce source brightness to an indirectly lit architectural space, while retaining the advantages of providing an optical control element close to the source of light for spreading the light. The invention provides an indirect luminaire having an upper exposed optical element in close proximity to the light source for controlling light distribution and for providing observable source brightness at viewing angles below the luminaire which is controlled to the point where flashing problems associated with a specular surfaces are virtually eliminated. The present invention also provides an exposed optical control element which can be readily modified to change the light distribution characteristics of the luminaire to meet different lighting application needs.